Data and control streams transmitted to a physical layer from a media access control (MAC) layer provide transport and control services through a wireless transmission link after an encoding process. A channel coding scheme is performed by a combination of processes for mapping error detection, error correction, rate matching, interleaving, and transport channel information and control information to a physical channel. Data transmitted from the MAC layer includes systematic bits and parity bits by the channel coding scheme.
The data stream may be transmitted in a state of being multiplexed with the control stream on the physical channel. In this case, control symbols of the control stream may overwrite a part of data symbols of the data stream. Then a part of the data symbols may be lost due to the overwritten control symbols.
FIG. 1 (a) illustrates a conventional method for mapping data symbols to resource elements (REs) of a physical transmission channel. Here, the ‘data symbol’ may refer to a stream of ‘bits’ which are generated when a transport block passes through a CRC attachment unit, a channel coding unit, a rate matching unit, and/or a code block concatenation unit or may refer to a stream of ‘symbols’ consisting of those ‘bits’. The data symbol may be coded symbols. The data symbol may be comprised of a systematic symbol and a non-systematic symbol. The non-systematic symbols may be a parity symbol. In a system using orthogonal frequency division multiplexing (OFDM), one symbol is mapped to one resource element and one symbol may be comprised of one or more bits according to a modulation order (Qm). For example, one symbol may be comprised of two bits as in quadrature phase-shift keying (QPSK) and may be comprised of four bits as in 16 quadrature amplitude modulation (QAM). If a binary phase-shift keying (BPSK) scheme is used, one data symbol may represent one data bit. Therefore, if the modulation order is 2, one systematic symbol may be comprised of 2 systematic bits. The same is applied to the parity symbol.
Each index of a buffer shown in an upper part of FIG. 1 (a) indicates one data symbol. As shown, data symbols are input to a cyclic buffer included in a rate matching unit of a transmission channel processor and output by a predetermined method. The cyclic buffer shown in FIG. 1 (a) may be replaced with any buffer in a multiplexing processor of a wireless mobile communication system. In FIG. 1 (a), data symbols from index 0 only to index 14 are exemplarily illustrated. Data symbols input and output to and from one cyclic buffer may include multiple redundancy versions which can be specified by a hybrid automatic repeat request (HARQ) scheme. Each index of the cyclic buffer may correspond to each of resource elements. Here, a set of systematic symbols consisting of one or more symbols, or a set of parity symbols consisting of one or more symbols is mapped to the resource elements.
In more detail, FIG. 1 (a) illustrates a conventional method for mapping the data symbols to a physical transmission channel on a resource element basis or on a symbol basis. In FIG. 1 (a), n data symbols are directly mapped to a multiplexing block buffer within n multiplexing blocks. Indexes of the buffer within the multiplexing block may correspond to respective resource elements one by one. Here, being ‘directly’ mapped means that n successive data symbols are successively and sequentially mapped to the multiplexing block buffer.
FIG. 1 (b) illustrates a conventional multiplexing method. As in the method of FIG. 1 (b), when n data symbols are mapped to the multiplexing block buffer, a control symbol indicating control information may be mapped, instead of the data symbol, to a specific position of the multiplexing block buffer. According to this method, the data symbols are sequentially mapped to the multiplexing block buffer. At this time, the data symbol is replaced with the control symbol at a position where the control symbol is mapped. Namely, the data symbol is overwritten by the control symbol.
FIG. 2 illustrates a phenomenon wherein a part of data symbols are lost during a multiplexing process.
Data symbols within any redundancy version may be comprised of, for example, one set of data symbols consisting of systematic symbols (index 0 to index 8) and one set of parity symbols consisting of parity symbols (index 9 to index 11) as shown in FIG. 2. Especially, in case of redundancy version #0, a probability of being configured in systematic symbols-parity symbols order.
Referring to FIG. 2, since a control symbol is mapped on a resource element RE5, a data symbol of index 5 of redundancy version #0 is not mapped on a resource element. The data symbol of index 5 in FIG. 2 is a systematic symbol. Accordingly, the systematic symbol is lost and thus an error rate for transmission data may be increased.
FIG. 3 illustrates a conventional structure in which code blocks for transmission are mapped to a physical transmission channel.
Referring to FIG. 3, 4 code blocks are used. Each code block may be comprised of output symbols output from the multiplexing block buffer of each of FIGS. 1 (a) and (b), and FIG. 2. As shown in FIG. 3, one transmission time interval (TTI) may be one subframe comprised of 2 slots. A physical transmission channel may be defined by the slots and frequency regions shown in FIG. 3. Each code block is separated into two blocks which are respectively mapped to the slots. For example, code block #0_0 mapped to slot 1 and code block #0_1 mapped to slot 2 are blocks separated from one code block #0. In FIG. 3, 4 code blocks are mapped by time division within one slot having a length of 0.5 ms.
Since the code blocks, for example, #0_0 and #0_1 use the same frequency band, multiplexed information of the code block #0 does not have a frequency diversity effect. The frequency diversity effect refers to an effect preventing a signal loss caused by frequency fading by transmitting signals over different frequency bands.
In multiplexing control symbols indicating control information with data symbols, the following may be considered. Overwriting systematic symbols among data symbols with control symbols (control information) should not bring about a serious effect. Moreover, a start point of a cyclic buffer for a next redundancy version should not be influenced by presence/absence of control information. Since the systematic symbols may be lost due to overwriting by the control symbols, an error rate should be decreased. Further, in an HARQ transmission scheme, HARQ buffer corruption should be avoided.
In a method for mapping transmission data or code blocks to a physical transmission channel, the following may be considered when transmitting data including control information. If the number of code blocks is small, loss of systematic symbols should be prevented. Conversely, if the number of code blocks is large, systematic symbols or parity symbols which are lost in each code block should be dispersed and should be equally distributed. In FIG. 3, if the number of code blocks is small, lost systematic symbols or parity symbols concentrate in a specific code block and if the number of code blocks is large, loss of many symbols occurs in a specific code block, thereby degrading performance of a transmission system.
In multiplexing control symbols indicating control information with data symbols, the following may be considered. If one transport block is comprised of one or multiple divided blocks (code blocks) and is multiplexed together with the control information to satisfy a predetermined transmission capacity, the amount of data included in the code blocks is decreased according to the amount of control information to be multiplexed. At this time, data overwritten by the divided control information may not be evenly dispersed to multiple code blocks and may concentrate in a specific block or specific blocks. Namely, since the overwriting or rate-matching control information may not be evenly dispersed with respect to each code block, the performance of a transmission system may be degraded. The overwritten or rate-matched data may be comprised of systematic symbols and parity symbols, systematic symbols, or parity symbols. Here, rate matching is used as a concept opposite to overwriting. That is, to rate-match control information to data indicates that the control information is inserted between data information. According to the rate matching, the data is not lost by the control information.